Feature #116: Shadow exclusion region

- Add --shadow-exclude-reg, which excludes certain regions on the screen
  to have shadows painted in. (#116)

- Adjust session initialization order. Now X root and screen info and
  basic X extensions are available in configuration parsing step.
Misc: --paint-exclude & #119

- Add --paint-exclude to prevent certain windows from being painted, for
  debugging purposes.

- Add predefined matching target "x", "y", "width", "height", "widthb",
  "heightb", "border_width", and "fullscreen".

- Fix bug #119, wrong man page install dir in CMake configuration.
  Thanks to sstewartgallus for reporting.